I just making board from poplar plywood about 400kg/m3 3x3mm because i didnt find balsa or pawlonia or red cedar (Please what it is pawlonian wood i cant find it in dictionary or wood atlas at this name). Board has about 1 cm continuos concave in middle and 0 at tip and rocker is 15 m diameter solid circle. It is 150 x 39 without flip tips and the core weight about 2kg. I now laminate it with carbon kevlar so i quest it will be weight under 3 kg board only . I built for this template from wood and gypsum bottom and top like form so i make blank very easy only laminate and put in the template and wait. It works great. My question: Can i use same rocker diameter with board with different lenght? For example 150 and 120 cm. With 15 m diameter this means 3,7 cm rocker on 150 and 2,3 cm rocker on 120.When yes i need only one template (form) and then i make it from beton.
And my second question how rocker diameter use you? I mean desired rocker on board not diameter on template.

Hi tomtom
The wood you are looking for is called Paulonia or Kiri wood, do a search on the internet for it and you will find lots of information.
Yes I use the same rocker for 3 sizes 140, 145 and 150, it is set at 3.5cm for a 145 which means it's a little less for the 140 and more for the 150.
I only use 0.5cm concave 1cm might be to much.
Remember to allow for the concave when setting your rocker.
By this I mean my 145 board has 3.5cm rocker and 0.5cm concave this means the the board has 3.5cm rocker on the rail 3.0cm rocker in the middle.

Only for your info Pete when you have solid circle you use exact 15m diameter rocker. Very funny me too.
Im talking about rocker on rails off course in middle is less

Thanks for answer Not annonymous too. I think that solic circle is fastes rocker shape see topic "best rocker shape". But is only theory i must try out it in real.

I will be very happy when you get me some /basic/ tip with vac bagging.

Pete why you thik that 1cm is too much?
I thinking in this way:
I have concave but only in middle and absolut flat tip. So i think that concave will press water under flat tail = press under tail witch means better and sooner plane. But maybe im wrong.

I actualy want only 0,5 cm concave but i make rocker/concave table with 1cm concave - because plywood springback. But, and this surprise me concave was set exact but rocker was smaller about 1/3. I compesate this by laminating.

So i try 1cm concave a i will see...

I also want try with me next board vacuum bagging but i have no experiences.

I want to ask you. Do you laminate deck and bottom with one step?
I do this in two first bottom and then deck. And how you overlap glas on rails?

Thank you very much for answer.

I will be never make this board without yours articles and experiences

Hi Tom
I think that your thoughts about the concave are right, but I am thinking of landing jumps to much concave makes it easier for the rail to dig in if the board is not dead straight.

I do a 2 step process bottom first the same as you, to get the wrap on the rail I wet out the glass then cut it about 1cm bigger than the board.
Next I use a layer of peel ply which I cut about 5cm bigger than the board.
Then I wrap both around the rail and use masking tape to hold it while I put it in the bag.

Vacuum bagging won't save you any weight when you are only using 1 layer of glass but it does make it easier to hold the glass nice and tight.

I actualy dont jump so much so i optimize my board for cruising performance (speed, upwind) We have gusty inland winds so i want quick plane efficient board and smaller kite rather than anchor type board for super overpowered jumping only. Im came from winsurfing and for me is speed cruising and carving very fun. I miss windsurfing speed very much. All production board i try (twintip) is too slow for me. So i try make real fast tt board. We have flat water so i dont make flip tips. What is my problem when the wind start blow and water is total flat speed is ok (on my curent plywood /not "real board" only wood/) but when water start be choppy speed begins decrease very rapid i think about half. IMO board start vibrate or somethig else because lack of rigidity. So i try make little stifer board /some flex is still here/ with concave and i will see. I send photo soon.

One else question. When you laminate and put laminanted core in to bag, you put whole thing on to rocker table again and weight or just laminate finished core?

I just laminate the core, you shouldn't need to put it back on the table.
If you want to make the board stiffer a small piece of 200g carbon fiber between the footstaps on the deck works best.
Cheers
Pete

Pardon me for dropping in , just a quick question.
Will putting down the carbon in the middle of the core while laminating work , instead of on top of the deck ? I ask this as I am not sure of my skill at the moment with dealing with carbon.

Putting the carbon right in the middle as in a 2 sheet build will make very little difference, putting it under the top layer of a 3 sheet will made some difference, but on the deck makes the most difference.
The idea is to increase the compressive resistance on the inside of the bend "the deck".
Carbon is no different to working with glass, it's just hard to see if its wet out properly because it's black, so be fussy with it.
I use a piece uni directional 300mm wide 200g carbon and it does the job nicely.
If you are using a vacuum to laminate your sheets then the easiest way to do it is to put the carbon on then.
When its set you can feather the edges with a sander before you lay up your glass.